1. Field of the Invention
The present invention relates to ink jet printing and in particular to an improved ink jet printer gutter design.
2. Prior Art
Ink jet printers are known in the art. These printers direct individual ink droplets to a recording medium along controlled paths to create a printed pattern. A typical ink jet printer can operate in an all character mode, all graphics mode, or a combined or mixed character/graphics mode. Ink jet printing architectures have improved to allow individual droplet resolution of approximately 300 ink spots per inch along the printed medium. The ink jet printer avoids the noise associated with a conventional impact typewriter and can operate with greater resolution and approximately the same speed as a so-called dot matrix printer.
Ink jet printers fall into two main architectural categories. The so-called drop on demand printers only generate ink droplets as the drop generator moves past a location on the print medium to be encoded with an ink spot. This type of drop on demand ink jet printer has perceived advantages from an architectural simplicity standpoint in that all that is required is a mechanism for controllably squirting droplets and some means for causing relative motion between the droplet generator and the paper to be encoded with the printed pattern. Perceived constraints on drop on demand operating speed, however, dictate continued interest in so-called continuous or Rayleigh-type ink jet printers.
The continuous type ink jet printer also comprises a drop generator for squirting ink droplets in the direction of a print medium. The continuous type printer, however, also includes means for selectively charging certain ones of the ink droplets as they are generated to allow their subsequent trajectory to be controlled. After selective charging of the ink droplets, those droplets are directed through deflection electrodes which create electric fields in the vicinity of the droplet trajectory. The deflection electrodes set up electric fields which deflect the ink droplets away from their initial trajectory depending upon the size and polarity of the charge induced at the droplet formation point. This deflection capability allows certain ones of the charged ink droplets to be deflected into a guttering mechanism so that only selected ones of the total number of droplets produced by the generator strike the print medium. In this way the continuous type printer generates a desired pattern of ink spots on the print medium. The architectural design of the continuous type printer is significantly more complex than the drop on demand system. Droplet charging, deflecting, and guttering apparatus is now required and in most ink jet printers of the continuous type, an ink recirculating system is needed to process ink droplets which are guttered. Once the recirculated ink has been processed, purified, and de-aerated, it is routed back to the droplet generator for another pass through the system.
In accordance with one continuous of Rayleigh-type printer design, those ink droplets which are to be guttered and recirculated for subsequent use are left uncharged at the droplet formation stage of printing. Those droplets intended to strike the paper or print medium are charged to varying degrees depending on their intended position on the medium. As these charged droplets pass through the droplet deflecting apparatus, they are deflected away from their initial trajectory past the droplet gutter to strike selected portions of the paper. Since during a typical printing operation, the majority of generated droplets do not strike the paper, this architecture results in a stream of guttered droplets passing directly into the droplet gutter while certain ones of the droplets are deflected away from this trajectory to a print medium. The number of gutters required for recirculating the ink varies with the architecture. Single nozzle ink jet printers are known which traverse back and forth across the paper width and therefore require only a single droplet gutter. Other architectures utilize multiple nozzles spaced across the paper width with each nozzle having its own individual gutter for recirculating droplets.
A problem with prior art ink jet printers has been clogging in the droplet gutter area. If ink accumulates inside these gutters and is not drawn away from the gutter entrance, ink droplets impinging upon the clogged gutter will break up at the entrance causing a misting problem in the vicinity of the droplet path of travel which can foul other apparatus comprising the printer as well as degrade image appearance on the paper. As well, the clogged gutter can cause ink to overflow into the deflection plates and cause shorting.
One prior art solution to gutter clogging problems was the introduction of a vacuum into the ink processing loop downstream from the droplet gutter which caused ink droplets and ink in the gutter to be attracted away from the gutter entrance into the ink processing portions of the recirculating processing loop. The problem with this technique is that the air rushing into the gutter causes the droplet not directed to the gutter to flutter, or vary from their intended path.